Update Ghost stack.yml to have persistent data (#2370)

ghost/stack.yml

@@ -18,9 +18,17 @@ services:
       url: http://localhost:8080
       # contrary to the default mentioned in the linked documentation, this image defaults to NODE_ENV=production (so development mode needs to be explicitly specified if desired)
       #NODE_ENV: development
+    volumes:
+      - ghost:/var/lib/ghost/content
 
   db:
     image: mysql:8.0
     restart: always
     environment:
       MYSQL_ROOT_PASSWORD: example
+    volumes:
+      - db:/var/lib/mysql
+
+volumes:
+  ghost:
+  db: